1. Field of the Invention
This invention relates to the production of composite shaped articles having a hydrophobic component and a hydrophilic component. More particularly, this invention relates to a process for producing fibers, filaments, yarns, films and other shaped articles in which the beneficial characteristics of both components, such as strength and moisture absorptivity (moisture regain), are combined.
2. Discussion of the Prior Art
It is known in the art to blend natural moisture absorbent or breathable types of natural and modified fibers, such as cotton, wool and rayon, to "comfortize" textile goods made from "dry" fiber types, such as the synthetic polyesters, polyolefins, polyamides and the like, to improve wear and feel characteristics.
It is also known to form shaped articles from blends of two or more polymers to obtain products combining the properties of both polymers or to achieve specific properties and effects. However, it is difficult to form such products from polymers having greatly disparate physical properties in view of the tendency of the polymer blends and resulting articles to separate into different phases.
U.S. Pat. No. 3,323,978 to Ole-Bendt Rasmussen discloses artificial textile fibers prepared by film to fiber technology from a blend of hydrophobic (major component) polymer and hydrophilic (minor component) polymer. As described in this patent the fibrous product has a two-phase structure including a continuous core portion of an oriented, normally crystalline, predominantly hydrophobic polymer, and a discontinuous surface portion of a different distinctly hydrophilic polymer. According to this patent a blend of the two polymers (or a potentially hydrophilic form of the hydrophilic polymer) is formed into a film. The film is stretched to orient uniaxially the crystalline hydrophobic polymer component. The stretched film is then contacted with a swelling agent for the hydrophilic polymer and the film is then split into a fibrous article having the two-phase structure described above. This process is dependent on the orientation forming a fibrillar two-phase microstructure of the hydrophobic and hydrophilic components, with the subsequent swelling treatment weakening the hydrophilic fibrils so that the splitting process will mainly be in the hydrophilic substance whereby the resulting fibers will have an accumulation of hydrophilic polymer at the surfaces. However, it has been found by subsequent follow-up work of this technique that the use of a swelling agent is detrimental in that, although facilitating longitudinal splitting and fibrillation, it also increases the tendency for crack formation.
Another drawback of the composite fibers produced from the polymer blends as disclosed by Rasmussen is that in view of the widely different molecular structures of the hydrophobic polymer and the hydrophilic polymer the resulting composite fibers show a pronounced tendency to separate at the interface between the hydrophobic and hydrophilic polymers upon repeated bending or flexing.
Accordingly, it is an object of this invention to provide an improved process for forming composite fibers from hydrophobic and hydrophilic polymer whereby the moisture regain properties of the composite fiber is substantially higher than that of the hydrophobic polymer.
It is another object of the invention to provide such a process wherein the resulting composite fibers have improved mechanical properties and stability in addition to high moisture regain.
Still another object of the invention is to provide composite fibers composed predominantly of a hydrophobic polymer with a discrete surface layer of a hydrophilic polymer and which is able to withstand repeated bending or flexing without undergoing separation of the polymer components.
Still yet another object of the invention is to provide a process which forms a composite hydrophobic polymerhydrophilic polymer fiber using the film-to-fiber technology but without requiring use of a swelling agent.
The above and other objects of the present invention have been accomplished based on the discovery that a similarly structured hydrophobic-hydrophilic two-phase composite fiber structure can be obtained without the use of any swelling treatment by stretching a laminated or coated film composed of a layer of hydrophobic polymer and a layer or layers of hydrophilic polymer and directly fibrillating the stretched laminate.
It has further been discovered that by providing a very thin layer of a compatible adhesive binder between the layer of hydrophobic polymer and the layer or layers of hydrophilic polymer the tendency of the different polymer components to separate upon repeated bending or flexing is substantially reduced or eliminated. Furthermore, it has been found that the presence of the thin binder layer does not interfere with the longitudinal splitting or fibrillation steps of the film-to-fiber procedure.
The present invention, therefore, provides a process for producing new types of fibers, as well as filaments, films and other shaped articles, in which a hydrophilic polymer component is intimately and stably associated with the surface of a hydrophobic polymer component so as to provide a wider range of properties than possible merely by blending equivalent amounts of the two polymer components.